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Starting Off My Career as a Pilot
I am 17 years old and am interesting in pursuing a career as a pilot. I am not sure what I need to do first, but I do have a flight lesson this Saturday to see if I want to continue with this career plan.
To start off, what certificate should I work toward first and where should I go from there? I have read about the recreational pilot's license, as well as some other licenses, and was wondering what I should go for first.
Also, any links to study material for any exams I may need to take would be greatly appreciated! All of the information about becoming a pilot seems a bit overwhelming, so I am just looking for a place to start and a basic plan.
Thanks!

You must be excited to start, but Saturday is not far away. You will be able to talk face to face to an expert then who will outline everything that you need to know. They don't expect you to turn up knowing everything, so just relax and create your plan after this lesson.

Welcome to aviation.SE! It's great that you're planning your first flight and I hope it goes well! Your questions are good ones, but unfortunately they aren't a good fit for this site: this is a Q&A site, not a discussion forum, and we like individual questions that are clear, specific and answerable. Yours is quite broad, and also likely to generate opinions and discussion; the [tour] can give you more information on how the site works. But feel free to post any specific questions you have, and we have lots of questions already that might be helpful for you.

What country are you in?

He selected the "faa-regulations" so that says USA to me.

Getting all the way from zero to everything you need to be a commercial pilot working for an airline is a major undertaking, both in terms of money and time. Don't rush it! It's great to have a goal to strive toward, but for now, enjoy that first flight for its own sake, then see where it takes you.

If you're considering going career, skip Sport and Rec; you'll need Private before anything higher, and there's no credit for having anything lower first. But wait until you see how your first few lessons go before getting too far ahead of yourself.

There are many  sources of information.
https://www.faa.gov/training_testing/testing/media/questions_answers.pdf
Reading the FAR-AIM, available at many flight schools is one good source, as many of the FAA Knowledge Exam questions come from this book.  There are online courses you can take, examples:
http://ww1.jeppesen.com/main/store/product_details.jsp?id=prod220010_ca
https://www.sportys.com/pilotshop/learn-to-fly/private-pilot-learn-to-fly-course.html
https://www.kingschools.com/
and many flight schools also offer Ground School classes.  You will need an instructor signoff to take the knowledge exam.
There are also flying colleges, such as Embry Riddle in FL. https://erau.edu/
I personally (1994, in my 30s) studied with Jeppeson materials and the FAR-AIM.  Being a college grad made the studying easy, being an engineer made the math calculation parts easier.  Anything I could not figure out, I quizzed my flight instructor on during flying lessons. The knowledge exam questions were available in booklet form then, I made sure I could answer every question, which often meant knowing where to find the information. Some things you just have to memorize, there is no way to work out/derive an answer. The exam was 60 questions out of the 700+ list of questions.
Try to find a way to fly at least twice a week if you can. Once a week you barely advance from lesson to lesson, missing a week for weather or something and it can feel like you went back 3 weeks. Being 17 will probably help with the motor skills for flying, but may hurt you on the learning part, depends on how good of a student you are.


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Wheel or skid? Which advantages does each one have when used as the landing gear system compared to the other one?
I would like to discuss this topic in depth, as I have not found a clear answer yet.
Which are the advantages of using skids instead of wheels (or viceversa) for the following considerations?:
-As the nose landing gear (case: Dream Chaser)

-As the whole landing gear (case: Eurocopter HH-65 Dolphin (wheels) VS. Bell 205A-1 (skids)

A skid as a nose landing gear is very uncommon. They exist (mostly on very old aircraft) in taildraggers. The helicopter choice is more straight-forward.

This is really 2 separate questions, as moving skids have very little to do with helicopter skids.

It really depends on how you intend on landing the vehicle, how you intend on using the vehicle, and generally any design limitations that may come into play.
For fixed wing aircraft that need to land with a forward velocity you can chose either skids, wheels or a combination of both.
Skids are beneficial as they are, simple, light and take up less space than conventional wheels as discussed in reference to the X-15

The aft landing skids have been questioned many times. But if you can
  figure out how to put a conventional gear into a 5-percent-thick wing
  and struts long enough to reach the ground in the landing attitude
  without losing the back end of the fuselage, be my guest! The current
  skids were located, as you will note on other figures, as the best
  solution to a difficult problem from a weight, temperature, and
  simplicity point of view.

However with a front skid you lose the ability to have nose gear steering and must resort to differential braking (assuming rear tires). With skids all around you lose ground steering and may possible damage the runway. For space craft this is typically not an issue as they are usually towed off the runway anyway. In the case of the Dream Chaser their may have not been enough space to stow a nose wheel.
Skids generally dont allow for any mechanical braking method to be applied. This means that you need to rely on aerodynamic braking like a drogue chute or reverse thrust.
Below certain airspeeds, with only skids you also lose all ground steering which can be an issue.

Wheels preserve steering and generally allow the craft to be moved off the runway easily. However this comes at the cost of added complexity, added weight, and generally added size. Since the space shuttle we have gotten pretty decent at putting landing gear on orbiters and at this point we know how to do it. While the tires need to be a bit different than your average car tire many aircraft tires are highly specific anyway. This question may also be of interest on the topic.
Spinning wheels, generally speaking also allow for braking to slow the aircraft after touch down. For short runway operations this is a must, since rolling to a stop is often not an option.
Wheels are generally beneficial for your average powered aircraft since ground maneuverability is needed to get around the airport and tires allow good braking ability.

Helicopters are a bit of a unique case, since they have the ability to hover and land vertically they don't really need any landing gear beyond a flat bottom. Wheels make it easier to push or tow a helicopter around the ramp while skids are simple and require little service on a helicopter.

The obvious one: when you land an airplane on skids, the skids abrade. This makes skids suitable only for aircraft which fly only occasionally (like the Dream Chaser): if you have 6 flights in a year, the maintenance on the skids is acceptable. For daily flights, not so much.

It turns out a skid is the safest option. There are potential issues with tires in the space environment and this eliminates one of the tires.

there will be one major difference when the nose is pitched forward, given the Dream Chaser will not be using a traditional Nose Landing Gear (NLG) wheel for its rollout. Instead, and inbuilt skid strip will touch the concrete floor of the SLF [Shuttle Landing Facility].
SNC [Sierra Nevada Corporation] have previously noted to NASASpaceFlight.com that this system is a simple, light, safe option. They also added that there had been some issues with the analysis of the performance of tires in the space environment and this eliminates one of the tires – with the other two tires easier to control than the nose wheel if there’s a problem with one of them.

THe article goes on to say:

“Just like the space shuttle Orbiter vehicle, the performance of landing gear system must perform flawlessly for the safe return of the crew,” added CCP (Commercial Crew Program) manager Ed Mango, who has previously worked in the Space Shuttle Program. “It’s great to see that SNC is building on that experience while developing the Dream Chaser spacecraft.”

https://www.nasaspaceflight.com/2012/07/dream-chaser-nlg-skid-system-landing-tests/

Helicopter specific answer
As a vary general rule, any smaller [less than 10 passenger] helicopter designed for general utility etc. work will often have skids, conversely large helicopters, military, VIP and Naval helicopters tend to have wheels.
Skid Gear is great for landing in softer terrain, it gives you a platform for people working from the side of the helicopter, more robust and cheaper for training aircraft among outer things, the issues with skid gear come as you enlarge them. If you land a helicopter with 7 ft long skids, you need about 7 and a bit feet of relatively flat ground to balance your self on, now if your skids are 40 feet, the issue becomes more apparent. Additionally skid gear helicopters which are on the ground are usually pushed [by hand] with small ground handling wheels, or some sort of platform, with larger helicopters this becomes more cumbersome.
Wheel gear has a few advantages over skid gear in some situations. Often wheels can be retracted, reducing air resistance, and increasing the cruising speed. In an application where you need to operate a large helicopter near other aircraft [or anything really] wheels are essential to be able to taxi, without flipping all the small planes, ground vehicles and ripping roofs off small hangers. In situations where there are small smooth landing spots where it would be really bad to slide off, such as and oil platform or pitching ship, rubber grips much better then steel. in rocky terrain, larger skid gear aircraft may have trouble finding a spot to put too long skids, where as a wheel gear only needs 3 well positioned places to put its wheels. Last, small helicopters do not need large skids, so the skids can be very light, and the complexity, cost and extra weight of adding wheels and shocks may not be worth it, but as a helicopter grows, so must the skids, at some point the wheels are lighter than skids.

Re tailskids versus tailwheels--
Tailskids are inferior to tailwheels for directional control on hard-surfaced runways, even if said tailskids are steerable.  Of course this is a negative advantage (disadvantage), not an advantage.
(Re steerable tailskids-- see https://en.wikipedia.org/wiki/Conventional_landing_gear )
Especially on a grass or dirt surface, a tailskid would tend to provide more braking action (deceleration) than a tailwheel with no braking mechanism.  In most cases this would be an advantage-- especially if the aircraft has no brakes on the main wheels-- but not at the start of the take-off run!
Many aircraft have used skids rather than wheel/s for the main landing gear to save weight and reduce complexity.  These skid(s) may either be retractable (e.g. X-15) or fixed and faired into the fuselage (e.g. many vintage gliders, and ME-163 Komet.)  In many cases there is also a pair of wheels on a short axle, or some other sort of "dolly" arrangement, that is used for take-off but then left on the ground or jettisoned shortly after takeoff.
It could be argued that the failure of the Wright brothers to appreciate the advantages of wheels over skids for routine usage was one of the significant shortcomings in their visions for how aviation might best progress forward, pioneering aviators though they were.

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Does thin airfoil theory work at very high angles of attack?
Thin airfoil theory says that lift coefficient is directly proportional to the angle of attack in radians. I haven't been able to find any limit, short of stall, for applying this theory. It would give us a huge lift coefficient at 90 degrees, where lift is actually zero, and double even that at 180 degrees, where again the lift is zero. This is basic reasoning. So, what am I missing?

What makes you think there should be another limit than stall? That seems like a pretty definitive limit to me.

Of course not. Thin Airfoil Theory produces a beautiful result that relates the zero-AOA lift to the mean camber of the airfoil, as well as the lift slope vs AOA of any thin airfoil is $2\pi$. But that's assuming:

Airfoil is asymptotically thin: such that the mean camber line represents the flow path
Camber is close to the chord: such that the vortex sheet is assumed to lie on the chord while resulting in the flow path that lies on the camber line
AOA and camber are small: such that all angles are linearized ($\sin\theta \approx \tan\theta \approx \theta$); obviously at large angles, this assumption breaks down and the results are worthless
Potential and incompressible flow: by the virtue of irrotationality, stall will not be modeled.

So in all, the result is only valid for small range of AOA on an idealized thin airfoil. For engineering purposes on general airfoils, you'd want to use panel method + boundary layer equations. But even then, extrapolating results beyond stall lead to ridiculous results (certainly at 90deg or 180deg).
More details on Thin Airfoil Theory can be found in Drela, Flight Vehicle Aerodynamics or Anderson, Fundamentals of Aerodynamics.

AOA and camber are small thanks! So that explains why my simulated plane is climbing straight up!

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Does jet engine exhaust velocity relative to itself remain constant despite speed changes?
Maybe this is a stupid question.
I seem to have been told, the velocity of the exhaust leaving an airbreathing jet engine relative to the engine, is constant despite changes in airspeed. However, to my understanding:

The ram effect causes air pressure to rise within the engine.
This higher pressure can then be converted right back to velocity with a nozzle.
This velocity adds to the velocity given by the fuel.
For an airbreathing engine with no friction or other losses in the ducts, this means that the exhaust velocity relative to the engine increases with airspeed.
meaning that the reason why we use low-bypass turbofans for supersonic aircraft is to reduce weight and intake losses, NOT propulsive efficiency
and this is what is shown by some attempts to develop low-loss supersonic through-flow turbofans of higher (around 2) bypass ratio.
in short: the statement only makes sense for rockets, which carry their own reaction mass, not airbreathing engines, which ingest reaction mass with any kinetic energy it contains, which cannot simply disappear.

So, what am I missing?

Thrust is created by accelerating a working mass in opposite direction. Net thrust is the difference between the impulse of the air flowing towards the engine and the combined impulse of burnt fuel and the air exiting the engine (and propeller, if one is fitted), derived by time. That impulse is the product of mass and speed.
When flying faster, the entry impulse of a propeller or a fan quickly grows large relative to the exit impulse, so thrust goes down with the inverse of speed. On the other hand, the high exit speed of a turbojet results only in a small increase of the entry impulse relative to the exit impulse while speed increases.

GSP simulation of a turbojet engine for varying altitude and speed, taken from this answer.
But if that were all, even the thrust of a turbojet engine would drop when speed increases. But there is a second effect which helps to let thrust grow with speed. With the square of speed, to be precise. That is the ram effect which helps to precompress the air entering the engine. At subsonic speed, this just about compensates for the loss of thrust: At low speed, the growing entry impulse lets thrust drop a bit but at higher subsonic speed the ram effect becomes larger and raises thrust again, such that a constant thrust becomes a good approximation (see simulation result in the plot above). However, pressure and thermal limits inside the engine will quickly limit the additional compression in the compressor and the amount of heating that can be added in the combustor. What helps is to fly higher, where outside pressure and the intake temperature will be lower, which more than compensates for the pressure and temperature increase from the ram effect. But then thrust will drop in proportion to density.
So far for turbojets.
Turbofans are a different matter. Here, thrust drops with increasing speed similar, but less severe, as it does in propellers. The nozzles of both the cold outer and the hot core flow only allow the exit stream to leave at subsonic speed, so at cruise speed the fan nozzle is critical or close to this (meaning, exit speed is nearly the speed of sound). In both nozzles the speed can not go up indefinitely and when the core engine exit speed at maximum thrust and low flight speed is already close to the speed of sound, the rule that it stays nearly constant is a good approximation of reality.

Uninstalled thrust and SFC for a large turbofan, from "Airplane Aerodynamics and Performance" by Jan Roskam. Found here.
The steeper trend of the sea level thrust line above Mach 0.7 is caused by the pressure limit of the engine.

thanks for answering my repetitive questions on this topic. I have one thing to clarify: are you saying that the thrust (and SFC, as discussed in our previous chat) limiter at high mach and altitude is the fan nozzle's inability to accelerate flow past mach 1, wasting pressure gained from ram effect as above-ambient pressure in the exhaust?

@ABJX: There is not much waste - pressure rise in the fan is held low in order to limit acceleration. On a high bypass ratio fan the pressure ratio is as low as 1.2 - 1.3.

That is for the fan nozzle, right? You say that the core chokes at very low speed.

@ABJX: No, the core flow doesn't choke at low speed. But it cannot accept arbitrarily large amounts of heating because then it would choke.

when the core engine exit speed at maximum thrust and low flight speed is already close to the speed of sound ?

Also, by "speed" I meant speed of the aircraft. Just so you can be sure.


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In theory, can jetliners remain controllable after losing the entire tail section?
The scenario here is a detachment of the tail,one with the whole empennage.
Could a variant of an existing model of swept winged jet airliner be made to remain controllable, using ailerons, differential flaps, differential spoilers and differential thrust, used for pitch, roll and yaw, regulated by an appropriate autopilot program, and with no other modifications?

If you could move the ailerons symmetrically: Maybe. But landing will happen at suicidal speed.

Reminds me of an accident in a Beeck V-Tail airplane where parts of the ruddervator were lost in flight.  SEA07LA118.

Theoretically, if the Neutral Point was still aft of the C of G with the tail gone, you could still be statically stable to some degree, but without the trimming surfaces of the elevator/stab providing the pitching force-balance system to control AOA, you become statically stable about the wing's zero-pitching-moment AOA somewhere, and you are more or less a lawn dart or a bomb and will arc down until in a statically stable vertical plunge.
You are unlikely to be able to make the wing, as it is, provide the required trimming power that was being provided by the tail. You might get some pitching authority by making the existing ailerons work together as elevons, but amount of pitching/trimming power would be so limited, it would only give you some control over your impact point, like a laser guided bomb, or at best, make it possible to maintain level flight at very high speed.
For that kind of concept to work, you would need to effectively reconfigure the aircraft as a flying wing, with all of its limitations, by incorporating all of the required pitch control and trimming authority for the full flight envelope into the wing itself, which means you have to design a new one, with a different airfoil and appropriately sized elevons at the wing tips, a limited C of G range, and all that sort of thing.
Then, on to your flying wing you stick a fuselage extension with a tail surface, for which you must also add fuselage forward to balance out, and you have a kind of weird hybrid tail-less-airplane-with-a-tail, like the evil genius farmer who bred a cow-chicken hybrid to provide a unified solution to eggs and milk production.

I just remembered Turkish Airlines flight 981. They were in an elevator plunge, but very nearly levelled off by increasing the powerl

But this had still the stabilizer itself, only lost the controll surfaces (or better: controll of the controll surfaces)

Yeah they were stuck with whatever trimming power was being provided by the stab setting and a limited amount of pitch change authority by varying wing engine thrust, where more thrust gives nose up trim.

No - though the vertical stabilizer might be worked around, the same is not true for the horizonal stablizer. Without it you will loose stability in the pitch axis so much that I doubt there will be any chance for a controlled flight on nearly all aircaft (though there is a possibility that a few ones might remain some kind of controllability)

Yeah, there's little pitch leverage. But I was wondering if sweep brought in enough to steer the airplane to a crash landing

Down-voted for being incorrect!

Even if you can still control the plane without the vertical stabilizer, is not the same for the horizontal one, as said by tsg. This because the wing is instable and has the tendency to dive the plane. The function of the horizontal stabilizer is to contrast this tendency. And no matter if the plane is statically balanced because this torque is due to the asymmetry of the foil wing.
The only chance is the that liners have arrow wing configuration. In this way the more external edges of the wing are in a back position in respect to the GC, and they can have still a stabilizing effect. This is why flying wing aircraft as B2 Spirit can fly. Maybe that this effect can be enough for some aircraft but not for someone else. In any case, also if the aircraft remains stable (without doing a crazy looping), it still remains the problem controlling the height without the elevator using only the engines.

You are (probably) correct that no actual/current airliner could realistically survive, but it IS possible to design one that could.

@MikeBrockington. It could also depend on the extent of damage eg the more tail is lost the more CG moves until aircraft becomes stable

Without the Vertical Stabilizer? Probably - but it would be very difficult. Without the horizontal, on the other hand, is a no. The horizontal stabilizer works by creating lift in the opposite direction of the wings. Moving the elevators or trimming increases and decreases the amount of "upside-down" lift, which moves the Center of Lift back and forth along the aircraft. Think of the airplane as a seesaw, the Center of Gravity is the fulcrum, and the Center of Lift is the force applied to tilt it. Assuming the nose of the plane is pointing to the left. If the Center of Lift is to the right of the centre of gravity, the aircraft will pitch down (if you pulled the right side of the seesaw up, the left side will go down.) Conversely, if the CoL is to the left of the CoG, it will pitch up. Without this stabilizer, you would have no way to move the CoL. Yeah, you can adjust the amount of lift from the wings, but you can't pitch.
Here's a great video on how the horizontal stabilizer works:

Look at the old-fashioned "free-flight" model airplanes from before the days of radio-controlled models-- they nearly all have lifting tails, with obvious right-side-up airfoils on the tail surfaces.  So clearly stability is possible with such an arrangement.  Take the idea to an extreme and you have a "tandem wing" configuration with similar-sized surfaces in front and back, then take it even further and you have a canard configuration.

@quietflyer It's possible if the aircraft is made for it. I can't think of a modern airliner that uses this design, and the original question was about airliners losing their tails.

Well, it depends on what you mean by "a variant of an existing model" and "controllable".
Technically, provided the center of mass does not shift out of range when the heavy tail falls off, a tailless swept wing can in principle be trimmed to fly straight and level. It can also be given effective controls surface.
But could "a variant of an existing model" necessarily be given suitable mass distribution or control surfaces?
Does the need to reprogram the flight software count as "controllable"?
Choose your answer accordingly.

While longitudinal stability can be designed into the wing, lateral stability will be lost without the rear fuselage and tail, given the the remaining forward fuselage.

@PeterKämpf Do you mean directional stability will be lost?

@AdityaSharma Yes.

Well, loss of tail would move CG forward.  Unfortunately, the only hope is to lose the front of the aircraft too.  Loss of tail results in lawn dart, albeit a possibly directionally stable one.  Wing sweep actually helps lateral stability, and so would winglets!  (Could this have inspired Rutan?). A presto canard in front might save it (beamed in from an XB-70).  Science fiction, maybe, in reality, no.


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Should a runway overrun be expected if takeoff is begun with one-engine-out?
Multi-engine aircraft have enough power to successfully takeoff if one engine fails after V1. But what if, on a runway equal to the specified takeoff distance, someone decided to roll with one engine out? Are the airplanes specified be able to lift off before running out of runway?

Related: Can an empty 747-400 with minimal fuel take off on two engines?

Starting the takeoff run without having all the engines operating that your data assumed would be operating is such a monumentally bad plan that it's hard to list all the ways things could go wrong... over-runs, VMCG issues, VMCA issues, climb gradients, etc. What might work despite such a mistake with a light aircraft + 3 miles of dry lake bed (i.e. just like an engine-out ferry, just unintentional) probably would fail in a way that makes the evening news most everywhere else.

You will not achieve book performance if you don't fly with book configuration.
See the portion of DeltaLima's answer here, including emphasis added by me:

[Takeoff Distance Required] has the aircraft accelerating to V1, suffering an engine failure at V1 and then continuing the take-off. This take-off involves accelerating from V1 to Vr, lifting off, retracting gear while accelerating and climbing, reaching V2 and 35 feet at the end of the runway. The runway length required for this scenario is the Take-Off Distance Required (TODR). The higher V1 the lower the TODR. This because when V1 is higher the part of the scenario that involves accelerating on a single engine becomes smaller.
These calculations take into account aircraft weight, engine thrust, aircraft configuration and runway condition.

Takeoff Distance Required is defined as the runway distance necessary to accelerate on all engines to V1, then experience an engine failure, then continue the takeoff to 35 feet above the ground.
It is self-evident that accelerating on less than all engines will require more runway than accelerating on all engines.  Therefore you will not achieve the TODR numbers by starting your takeoff roll on one engine.


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Induced drag reduction from tandem wing
Induced drag is proportional to the square of span loading. The normal method to decrease it would be to increase span. This, however, leads to an exponential weight increase.
So, my question is, if tandem wings are placed with a large longitudinal gap, so as to avoid downwash, would they act as independent wing spans sharing the weight of the aircraft to reduce induced drag? If so, how large would this gap need to be? Would one at the nose and another at the tail be enough?

The downwash is as high as wide and goes down only a couple of degrees. s

The downwash is about as high as wide, and angled only by a few degrees (more at slow speed). So the longitudinal distance needs to be many times longer than the wing span to make the wings independent.
And it would still be less efficient than increasing the span:

If you double the span, you will decrease induced drag four times.
If you half the lift, you also decrease the induced drag four times, but then you add the second wing to get your lift back and that also doubles the induced drag, so you have half the induced drag, not quarter.

That's odd. I thought induced drag was to the square of span loading

@Abdullah, yes, inversely proportional to square of span loading. Square of two is four, and inversely proportional, so doubling span will reduce it four times. If you half the lift, you will also reduce it four times, but then you add the other wing to get your lift back, and that also doubles the induced drag, so you get only half induced drag, not quareter like in the first case. Which is logical, because you have only doubled the affected stream tube while doubling the span quadruples the affected stream tube.

https://aviation.stackexchange.com/a/36064/45534

@Abdullah, yes, I know that equation. I am basinc my answer on it. $D_i \propto \frac{L^2}{b^2}$. $\frac{L^2}{(2b)^2} = \frac14 \frac{L^2}{b^2}$, but $\frac{(½L)^2}{b^2} + \frac{(½L)^2}{b^2} = \frac{L^2}{4b^2} + \frac{L^2}{4b^2} = \left(\frac14 + \frac14\right) \frac{L^2}{b^2} = \frac24 \frac{L^2}{4b^2} = \frac12 \frac{L^2}{4b^2}$.

I just realized you're right


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For subsonic aircraft, would adopting a higher wing loading decrease drag?
First, let's assume that problems with approach/TO speeds can be fixed by high-lift devices.
Here we read that the wings create more drag than the fuselage. So, an improvement seems obvious; shrink the wings.
However, for a given weight, altitude, and airspeed, such a wing would need to fly at higher angle of attack, creating more induced drag. How does this compare against reduced parasitic drag?
If one wants to reduce induced drag, than one must fly at lower altitude. This means more parasitic drag - again. But does the former outweigh the latter?
Induced drag can be reduced further by the weight reduction from a smaller wing. How does this compare to the above?

You design to go as high as you can with sufficient thrust at that altitude to match the drag of a very large wing.  As critical Mach number is reached at a lower and lower IAS, the higher you go, the slower you go for the same TAS.  Limiting factor is passenger safety.  A sailplane configuration with a Concorde fuselage would be interesting.  It would look a little like a U-2 with windows.

Generally, you are right. Reducing wing area is reducing overall drag. Within limits.
Induced drag depends on speed and span loading. If the reduced wetted surface allows you to fly faster, induced drag will be lower, leaving more of the power budget to overcome viscous drag. However, if wing span is reduced, induced drag will be higher at the same speed, so it is better to reduce chord than to reduce span. This can be witnessed by the recent development in airliners where the reduced fuel flow of engines has allowed to build smaller wings with higher aspect ratios. A similar but older example is the Davis wing which combined extreme root airfoil thickness and an aspect ratio of 11 to minimize overall drag and keep wing weight reasonable. Other aircraft designed for long range even sported an aspect ratio of 14.5!

If one wants to reduce induced drag, than one must fly at lower altitude.

Don't focus on induced drag reduction alone! Please remember that the lowest overall drag is at the polar point where induced and zero-lift drag are equal. Move away from this point and overall drag for lifting the same weight increases.
Turbine engines profit from colder air. Flying higher means higher true air speed for the same dynamic pressure. Therefore, wing area should be sufficient to allow operation close to the tropopause. Going higher than that does not improve things, but staying well below the tropopause means to forego an obvious advantage. Only airplanes designed for low level missions will have a wing loading well above the 600 kg/m² which is typical for airliners. That's the limit mentioned above.

You might have heard of the "coffin corner" the U-2 pilots flew in. The U-2, at 90,000 feet, had only 9 knots between stall speed and Vmo. Airliners fly in a similar, but wider corner, with circa 15-30 knots between stall and Vmo. Vmo is where shockwaves start appearing on the upper wing surface, buffeting, engine surge and all kinds of bad stuff happen. Stall speed is relevantly high as low air density means the wing already operates at a high lift coefficient, also the wing has a lower CLmax value in transonic conditions.
The reason for this may not always be purely aerodynamic/stall related, aeroelastic behavior of the wing with high CL and transonic speeds is very complicated (even more so with complex wingtip devices) and I believe this will be the limiting factor.
For specifically designed wings, the wing can achieve higher transonic CL compared to subsonic, but I hugely doubt that an airliner wing is designed like that. Wings designed for high transonic lift are generally seen on fighter planes. As they have a lower aspect ratios and don't have wingtip devices, they are simpler from structural and aeroelastic standpoints.
Coming back to your question, the wing does not have much room to be shrunk, even in cruise conditions. Accommodating for the takeoff and especially landing is not as simple as slapping on high-lift devices, as in that case you'll still need to account for the failure of some high-lift devices and still be able to land the airplane.
The F-104 interceptor was designed with a very small wing (we had a F-104 gate guardian in front of our building in college, I was shocked when I first saw it with my own eyes) and resorts to flaps, slats and a boundary layer control system, which is air bled from the compressor to energize the boundary layer and delay the onset of stall. BLC obviously only worked when the engine was running, so with a flameout the approach speeds of the F-104 exceeded 200 knots. This was a contributing factor to the terrible safety record of the Starfighter, some air forces lost over 30% of the airplanes they acquired in accidents.


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Why will the 777X be tested for crosswind handling with wingtips raised?
Wikipedia says:

As existing regulations do not cover the folding wingtips, the FAA issued special conditions, including proving their load-carrying limits, demonstrating their handling qualities in a crosswind when raised

Why?
Especially when this question says:

The 777X family (777-8/-9/-10) features wingtips that fold up on the ground to let the aircraft fit in tight spaces. These have to be extended and locked in place before a revenue flight can take place,

So, what is the point of certifying the 777X for wingtip up flight? I haven't found a reason for this in Wikipedia either. Is it for ferry flights or something?

I'm unclear on what "raised" means, is that retracted or extended? The wingtips on the 777X shouldn't ever be locked in a "raised" position AFAIK.

@zymhan And I'm not sure what you mean by "retracted or extended"? I'm not a native English speaker, but to me these words don't make sense when talking about the 777X wingtip. Raised and lowered seem more intuitive to me.

@zymhan actually yes, it does sort of mean retracted, though the term would misleading in this case (I think). Anyway, pretty much anyone who's familiar with the 777X would know that a raised tip is a folded tip

Boeing also has to demonstrate “acceptable” handling qualities during crosswind conditions, even if one wingtip fails to completely fold. This would indicate that they are not simply looking at Open vs Closed.https://www.flightglobal.com/faa-sets-certification-rules-for-777x-wingtip/128151.article

@zymhan: Some parts of that article sound almost like a threat in hindsight, now we know what would happen only 4 months later: "As with any critical airplane systems, like flight controls, […] Boeing uses a hazard class determination for certain extremely improbable airplane level failure events to drive the appropriate high-integrity system architectures, design redundancies, and safety features to preclude such events,” Boeing says. “This same safety and certification methodology was used with our new folding wing tip […]" Oh really, they applied the same safety methodology as for MCAS?

@Bianfable the problem with "raised"/"lowered" is that it would be possible for them to fold downwards - then raised would be for flight and lowered for ground.  "Retracted"/"extended" needs less prior knowledge to make sense.  The older question quoted in this one is clearer than wikipedia in that regard

@ChrisH me asking why the 777X wingtips need to be certified for acceptable handling in the flight configuration would be stupid.....

@Abdullah it would, and I never suggested you would do that.  I was commenting on Bianfable's  preference for "raised"/"lowered", when without prior knowledge (that you clearly have) that pair doesn't define which is the flight configuration and which isn't

how'd I get a downvote?

If you read the details in the Federal Register, you can see that this refers to crosswind handling on the ground, not in the air:

The folding wingtips and their operating mechanism must be designed
for 65 knot, horizontal, ground-gust conditions in any direction as
specified in § 25.415(a). Relevant design conditions must be defined
using combinations of steady wind and taxi speeds determined by
rational analysis utilizing airport wind data.

And:

The airplane must demonstrate acceptable handling qualities during
rollout in a crosswind environment, as wingtips transition from the
flight-deployed to folded position, as well as during the unlikely
event of asymmetric wingtip folding.

Why is asymmetric wingtip folding "unlikely?" I don't think there is any mechanical connection between the two wingtips going right along the wing spars and through the fuselage which is strong enough to make it impossible that one moves and the other does not!

If they got it right this time, failure to raise or lower a wingtip will require more than one failure in the system responsible. (Barring extreme conditions like total absence of the wingtip) Which ought to be unlikely. Even in that condition the aircraft should be safe on the ground : hopefully they won't try to fly it like that.

@alephzero, there is no mechanical connection between flaps either, but the system still must prevent asymmetric deployment. This is similar.


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What’s that weird sound during spool up on some aircraft?
Some engines seem to make this characteristic “wailing” noise when spooling up. A good example of such is from 0:50 to 0:54 in the following video:

   . I’ve also heard it on a300s, 767s, and md-11s. Does anyone know the source of this noise and why it only occurs with certain engines?

Sounds very like it's hitting a resonant frequency

I like how excited the windshield wipers wave and cheer with unbridled joy.

That noise is almost exclusive to turbo fan engines.  If the air is right, turbo shaft engines can do it.
  On sudden and high power changes the big fan on the front is spinning at a different speed than the motor compressor.  Since the front fan is also the first couple of stages of the engine compressor, the air doesn't move cleanly between the two when they are not at the same speed, and make that sound.
The Navy S-3 made the same sound on power changes so it got the nickname Hoover.
@Rob,if you are close enough to it you can feel it.


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Does the FAA allow changing an aircraft's registered class?
For instance, if an aircraft is first registered as an airplane, can it later be changed to a glider or vice versa? How about a single converted to a multi?
(If you're wondering about why this could ever be a thing, imagine a homebuilt like a Sonex somehow converted into a Xenos.)

I am not sure, but I think once you get an airworthiness certificate it becomes very hard to change the class. But it is interesting to note that the FAA does not define a "glider" in the experimental category. A DER once told me that it comes down to how good a job the DER does of convincing the FSDO it should be one way or the other. Weird.


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Free baggage allowance: Weight concept vs Piece concept?
What are the advantages of piece concept free baggage allowance policy compared to the weight concept free baggage allowance policy in terms of contribution to the profitability of a commercial airline?
Which policy provides more load space in the cargo holds of a passenger aircraft and/or provides more payload to carry compared to the other or vica versa.

This question would be better answered on travel.SE

It also sounds like it may be a homework question

There are more rules involved here and the Airline can make a judgement call here which ever is more suitable for them.
Here at EHAM we have a limit that one person is only allowed to lift a bag of 23kg, if a bag is heavier it needs to be lifted by two persons thus increasing the processing cost for the airline. For aircraft the most important parameter is weight, more weight equals more fuel or, in extreme cases, less range. (range is traded for added payload)
So depending on the load factors of the aircraft and the amount of additional cargo the airline transports it can determine if it has the space available to transport more voluminous luggage by allowing multiple pieces that add up to 23kg per pax for example.
So there is no definitive answer possible to your question as there is a trade off to be made by the airline, filling the entire cargo hold with a high density material like lead is not possible, the aircraft would be too heavy.

"we have a limit that one person is only allowed to lift a bag of 23kg" I know that a lot of airlines have similar "rules", but I've yet to see a baggage handler ask for assistance in moving any luggage, even the ones very clearly marked "HEAVY".

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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Is there a Risk of Tail Tipping during Push-back of a passenger aircraft?
I remember that there were countless incidents occurred in which the aircraft sits on the tail as the aircraft was heavily loaded at the back of the cargo and/or cabin compartments or the cargo compartments were offloaded incorrect order. I know that these incidents are more commonly happen in cargo aircrafts.
Is there a risk that the aircraft will sit on the tail during the pushback process as a result of the tri-cycle design of the aircraft?
Is there any tail tipping incident reported during pushback/towing operation?
Which types of aircraft (narrow/wide body) can this risk be higher?

As far as I know the aircraft landing gear is required to carry at least 4 or 5% or even more for the most aft center of gravity position (I think it was for ground operations within the allowable takeoff and landing cg range). That means for a light 48t aircraft you still have 1.9t resting on the nose gear, forcing the nose down. Not that easy to push over....The risk of tail tipping is only present when the aircraft is being loaded where you get ugly transient cg changes but not when it is fully loaded and the cg range is back within calculated limitations.

Tipping could occur if pitch-up moment was created by braking with the main gear brakes. This is a risk in power-backing (using aircraft's own reverse thrust), but during push-back the brakes on the tug are used, so it shouldn't be possible.

Btw I saw a tip-over happen once of a non-flying 727 at a museum, after it got covered in freezing rain.  No idea if its CG was anywhere near the prescribed CG for flight, before the ice accumulation.

During pushback the (usually quite substantial) weight of the tug pulls the nose down, and additionally when it's pushing backward the line of force is below the CG and acting rearward, so that would also tend to counteract any tipover tendency.
As Jan mentions in comments, the tipover situations tend to happen during loading when the CG is moving around. I suppose if the tug were first attached and then the aircraft were grossly misloaded, it's conceivable that it could tip over backward as the tug detaches and removes it's weight, but I've never heard of that happening.


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Why are inflatable pillows not allowed on board?
Inflatable cushions designed to ensure extra space that children sleep comfortably between the passenger seats are not accepted aboard by most of the airline companies for they can obstruct evacuation in case of emergency situation. In my opinion, there is no safety risk for these accessories in case they are permitted to be used on a level flight(cruise phase). Is there any additional reason why airline companies do not accept similar products on board? What else can be the reason not accepting inflatable cushion like accessories on a flight. Does it really pose a safety risk and compromise flight safety in a level flight?

You answered your own question. What exactly are you looking for here?

Isn’t it unreasonable not to accept these accessories because there is no emergency evacuation in a level flight(I don’t mean that these accessories are to be allowed to use during taxi, take-off and landing phases). In addition, i try to understand the logic that some airlines are accepting and some others are not. What is the logic behind this?

I don't see what you want here. This isn't a discussion board, and even if it was, our opinions won't change airline regulations. I'm voting to close this as it seems to fall under "your question is just a rant in disguise: “_____ sucks, am I right?”_ - see [help/dont-ask]

@GolfCharlie Unfortunately, this is a legitimate question.  The answer may be linked to the effects of decompression.  Even under normal flight conditions, it is common to have cabin pressure lower than 14.7 psi.  In the event of a hull failure at altitude, "inflatable" objects would likely explode.  There for, restricting them is reasonable.

@GolfCharlie your assumption that there is no safety risk is completely incorrect. Three words make that so: Clear Air Turbulence. And that is just one example. If people are so worried about their children sleeping comfortably on a short flight, there are other options for travel, including private vehicles, buses and trains.

"they can obstruct evacuation in case of emergency situation."
Thats the reason.
"In my opinion, there is no safety risk"
Please describe your qualifications and level of expertise to have a valid opinion.
"Does it really pose a safety risk and compromise flight safety in a level flight?"
If an emergency occurs at cruising altitude, and the plane begins an emergency descent, emergency landing and emergency evacuation while the plane is on fire, is your first thought really going to be "I better be sure to deflate my kid's inflatable cushion"?I think you are more likely be pre-occupied with oxygen masks, seat-belts, smoke inhalation, holding your child, and running for the emergency exits.  You will forget all about the inflatable cushion.  It might well trap and kill people behind you during the emergency evacuation.

In order not to obstruct evacuation and affect other passengers comfort/safety, why it’s not allowed to be used only in mid seats(on wide-body aircrafts only) and in window seats (both narrow/wide body aircrafts)? Should it be understood that airliners that allow inflatable pillows are less safe?

They’ll be too busy grabbing their luggage, if recent incidents are any indication.


text:
Can 7 AKE containers adjacent to each other be securely locked in a 777-300ER's aft cargo bin?
Is it possible to securely lock 7 AKE (LD3) containers adjacent to each other in a Boeing 777-300ER's aft cargo bin from position 31 to 41 (41 included)?
According to my experience it's impossible to securely lock 7 AKE containers adjacent to each other if a partial load stop is raised between the containers.
If a ULD lock does not get raised between containers, then it is OK to lock containers using only an end-stop at the beginning of position 31 and raising the lateral guide located at the end of position 41 (between positions 41 & 42), but I'm a bit unsure of using such a combination and find this unsafe because there are only two ULD locks that secures 7 sequential containers.
Could somebody confirm whether is it safe to do so and/or can give detailed information on B777-300 ER cargo hold loading configurations, ULD locks and ULD loading rules?

The 777-300 ER weight and balance control and loading manual, D043W530-XXX1  has some of what you want.

@ymb1 thank you good sir! Coffee wasn't working this morning and I didn't see one.

This seems awfully specific for an "I'm just curious about how airlines do this stuff" question, and "some guy on the internet told me it was fine" isn't good enough if you're loading an actual plane.


text:
How should ground crews act to safely extinguish an airliner's brake unit fire?
When the brake unit was overheated and had just begun to catch fire due to excessive braking because of long taxi distance upon arrival, the ground personnel (not firefighters) made the first intervention with the fire extinguisher on the parking stand until the firefighters arrive.
I’m wondering, are there any points to be taken into account in terms of ground safety when approaching landing gear during this first intervention or in the case of extinguishing? Is there any guidance procedure for ground crew other than professional firefighters?
What type of extinguisher content should be used to extinguish the fire?

Regarding the related post: How do fire crews handle hot brakes?
I don’t think it’s the same topic. I would like to know if there is a guidance document explaining how the ground crew [not fire crew] should behave in the event of a brake fire upon aircraft arrival.

The main thing is the big rubber bomb around each of the wheel rims.  Hopefully the thermal fuses will work and let the air out without taking out any bystanders.  I wouldn't go anywhere near a burning wheel myself.  The firefighters are going to approach it with the foam/water cannon while inside the truck.

I don’t think it’s the same topic. I would like to know if there is a guidance document explaining how the ground crew should behave in the event of a brake fire upon aircraft arrival.

Possible duplicate of How do fire crews handle hot brakes?

@ymb1 Thank you for making it more understandable on my behalf.

Don't put yourself alongside the tire. The thermal plugs, if they blow, are going to blow outward from the tire. Stay in front of or behind the tires.

Why do you think it would be much, if any difference than fire crew guidance about approach path and water given to firefighters?

@Terry Dear Terry, thank you so much for the valuable information provided.

@Notts90 Firefighters are exposed to less risk than groun staff only because they are trained to acquire fire fighting skills and have protective clothing. So i’m just trying to learn how this issue to be handled in a safe manner from ground staff perspective.

@Terry Boeing says to approach at a 45 degree angle. My understanding is the wheel will tend to blow out to the aircraft's left-right axis, the tire itself will blow out foward-aft, so 45 degrees avoids both.

@user71659 Good info! In the 747 ground schools I attended, at least as I remember them, they didn't cover the tire blowing, saying that the thermal relief plugs would preclude the tire blowing.

Approach from upwind. The source of fire is hot brakes so apply maximum cooling, say water-based. But hydraulic fluids under pressure burn, so if brakes are engaged it's best to ensure with flight crew that the brakes are off as soon as the aircraft is stationary. Stay in the vehicle in case tyre ruptures; chances are it will go sideways. If fuel is leaking, use suitable foam.
I once saw a Harrier with a brake fire.  The burning pressurised brake fluid was acting like a flame thrower on the aircraft structure. The aircraft was written off. This happened about 1981.


text:
What are some alternate methods of communication with aircraft (specifically small drones)?
I've been thinking about his alot but I've yet to find an answer.
Most of the time drones use radio, wi-fi, GPS and Bluetooth signals to communicate with their controllers but all of these methods can easily be intercepted, espically radio signals.
Are there any alternate methods of communicating with drones and of there isn't, what are some ways to make it harder for other people to jam or intercept the signals?
Thanks.

'I've yet to find an answer' - there isn't a single answer. Even your question asks for 'some ways'. This is way too broad for a concise answer. Trying narrowing the focus to something more specific.

Wired communication, e.g. copper wire or fiber optics, are pretty much impossible to jam or intercept. Directional wireless communication, e.g. mmW or laser beams are also good choices. Radio can be made very robust, too. Wifi, 4G and Bluetooth are easy to jam because they are industrial standards that operates at known frequencies. In the military context, where the majority of concern for jamming occurs, doesn't have to follow industry standard or FCC/ITU regulations and operates at a much wider frequency range, hence hard to jam as well.

@user3528438 to your point, tethered drones do exist (e.g. mobile cell tower ) .

Interception is only a problem for unsecured communication.

I really don't like that question being answered.

You really seem to be starting from a position of extreme ignorance.  Wi-Fi and Bluetooth ARE radio signals, occupying particular parts of the frequency spectrum (and with modulation & encoding specifications).  GPS signals are likewise radio, but they are receive-only, so not really communication.  The only other halfway practical way I can think of would be to modulate the signal of a laser pointer, but that would require line of site and some pretty accurate pointing on your part.   And why would I jam when I have a shotgun?

Interception is not a concern when the communications are strongly encrypted.
Plaintext (unencrypted) communications are obsolete for all except for the most public purposes. The search request that led you to this site was encrypted. The page you're currently reading is encrypted, in a way that would take effort even for the NSA to crack, even though everything on this page is openly available to anyone in the world.
Wi-fi and bluetooth are subtypes of radio, and too short-range for a flying drone. GPS is actually effectively impossible to intercept, as it's all public and there's nothing to intercept.
Regardless, encryption takes care of the contents of your communications.
If you want to hide the very fact that communication is taking place, laser links are the only option that isn't easily detected through dispersion, sidelobes and reflections. High-frequency traders use laser links commercially up to about 10 km. This is reliable all-weather ground to ground range. Ground-to-air comms have been tested for up to 60 km on a clear day.
Fighter aircraft communicate with their jamming/decoy drones through a copper or fiber optics cable, which is also used as a tension cable for towing.


text:
Is it possible to create Interference Drag without physical surfaces conjoining?
Interference Drag is when boundary layers mix/combine, usually it's caused by pieces of metal conjoining (wing struts/gear retracting).
Is it possible for interference drag to be created without having physical surfaces connecting? Rather, is it possible for boundary layers to form/mix without a physical surface?

Can you clarify? Do you mean boundary layers with no hard surface nearby, or boundary layers where the hard surfaces are close but not touching?

Yes, there can be interference without the surfaces in contact. It isn't limited to drag but can also alter lift and stalling/flow separation.
Biplanes with closely spaced wings are the best example I can think of at the moment. Axial flow turbo fans and compressor blades are other cases. I remember some sort of smooth/bladeless turbine invented by Tesla that operated only on boundary layer interference between unconnected surfaces.
To be clear there is always some connection somewhere to maintain the separation distance. I really mean cases where the connection point is far removed from the area of interference.


text:
How to improve engine-out handling on a multi-engined aircraft?
Hypothetically, if I wanted to create a multi-engine airplane with the best single-engine handling characteristics/lowest Vmc, would moving the vertical stabilizer far back be beneficial (even if it looked weird)?
My school of thought is that: At low airspeeds, the rudder is less effective. If I can't increase the amount of airflow over the rudder, will giving the rudder a massive arm allow the plane to have more directional control at lower airspeeds with the increased torque?

Also there will be a torque arm that goes from each engine to CG.  So making the engines as close to CG can help reduce the size and arm of the tail.

Yes providing a longer vertical tail arm is very beneficial for control in case of engine failure.
During the pre-design phase of an aeroplane the Tail Volumes are determined: area of horizontal and vertical tail, times the moment arm. This answer gives more info on some statistical data and methods.
Of course, optimal dimensioning is paramount since we're dealing with aerodynamics and we want to limit drag. The tail arm is usually limited to the useful fuselage length, leaving the tail area to be the main design parameter.

The engines can be in push-pull configuration, or stacked on top of each other, to keep them on the centerline.  If that can't be done then simply put them as close to the centerline as possible.  Put more (presumably smaller) engines on the aircraft so that the loss of a single engine has lesser effect on performance.  A larger rudder further back would help also.
I recall reading about someone that built a custom light airplane to fly over the Amazon forest.  As I recall it was to take close up photographs of the canopy.  A concern was an engine loss over such a remote area, and in the low altitudes they'd be flying.  The plane had two pusher props close to the centerline and a larger than typical rudder.  This was so it could fly for extended periods on a single engine and not fatigue the pilot.  I also recall that they'd kill one engine in flight so they could fly slower and get better pictures, which in my mind negated much of the advantage of two engines.

Shutting down an engine in flight might save gas, but it doesn't "let you fly slower."  If anything, engine-out, you have to consider not only a margin above stall speed but also above Vmca.

@Ralph J: Consider the Rutan Voyager.

@jamesqf, Voyager was a pull-push configuration, which this apparently wasn't, and even that couldn't fly any slower on one engine.


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How to learn the back end of flight simulators?
I am an engineering student very passionate about aviation and especially flight simulation. I want to know more about how a flight simulator is coded but unfortunately there's not much available on the internet. I want to learn the software aspect of it and would appreciate some help being a complete beginner.
If someone could assist me answering a few questions or having a discussion regarding what language to learn or what books to read, it would be of great help.
Thanks in advance!
Cheers!

The most advanced open source flight simulator is currently FlightGear. It doesn't fall too far short of its commercial brethren.
The repository is hosted on SourceForge, where you can download the entire codebase.
For documentation and discussion on how it works, see the forum and the mailing lists.
Once you have questions regarding the codebase per se, especially regarding the technical implementation rather than the business end of the simulation, they are best asked on the forums or on the main Stack Overflow site. Aviation.SE mainly deals with the flying aspects and real-life aircraft.

Alright , thanks a lot for helping


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How much actual difference does fixed pitch propeller make in takeoff distance?
So it's possible to buy fixed pitch propellers which are either optimised for takeoff or for top speed. I guess most airplanes have a compromise.
Considering a training aircraft like a Cessna 152, what would be the difference in Ground Roll and Total to Clear 50ft obstruction between different props?
As an example the Ground Roll and Total to Clear 50ft Obstruction  at 20 deg C for a weight of 1670 lbs at Sea Level is listed as 755 and 1390 feet respectively. How much numerically  would they change with different props?
Please note this is just a hypothetical question. I'm not in the market for propellers!

Between a cruise prop and climb prop, takeoff performance will generally improve about 15-20% with the climb prop vs the cruise.

With my old VariEze (not a training aircraft; in the same power class as the Cessna 152 but lighter and with much higher wing loading) I had a cruise propeller and a climb propeller that I could exchange on the ground with about 30 mins of work. I measured ground roll at max gross weight and calm wind to be around 1500' with the cruise prop and 1100' with the climb prop. I could usually get around 1500 fpm climb with the climb prop and 1000 fpm with the cruise. Cruise speed was 10 to 15 kts slower with the climb prop depending on altitude; you'd usually have to throttle back quite a lot to avoid exceeding redline RPM.
The difference in takeoff performance is more dramatic when a constant-speed (variable pitch) prop is compared to a fixed-pitch prop. I'm presently in the process of upgrading my Lancair 360 from a cruise/climb compromise fixed-pitch prop to a constant speed and I expect that to decrease the ground roll to less than half the current 1500'. I'll report back with data once it's flying.

Why would the takeoff performance of a constant speed prop be any better than a fixed pitch climb prop that is optimized for take off RPM?

@mikesowsun The constant-speed prop can go to finer pitch than the climbiest of remotely-practical climb props. This gives you significantly more thrust for the earlier portion of the takeoff run while the aircraft is below flying speed.

The CS prop runs at redline the entire time so you are getting full rated power for the entire takeoff roll.  Even a climb prop has to either be pitched to keep RPM below redline at low speed. If you pitch it fine enough to get redline at the start, you have to reduce power as soon as you are rolling to keep from overspeeding.

@pericynthion +1 for "climbiest"


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Which countries (if any) allow beyond-line-of-sight drone use?
I was recently thinking about starting up a non-profit that would use large drones (full scale aircraft, not those dinky quadcopters) to deliver humanitarian aid to difficult locations.
It was shot down pretty quickly when I remembered that civilians aren't allowed to fly unmanned systems beyond [the visual] line of sight (BLOS).
So, this led me to my question, are there any countries that allow BLOS use of civilian unmanned aircraft?

Don't stop pursueing a good idea because current day regulations are blocking. They will change. BLOS will be used for this kind of purposes. There is work going on to integrate this class of UAV's in the ATC system. This is not for dinky quadcopters but for unmanned aircraft that are certified to meet many requirements  before the are allowed for BLOS. There is a clear move into that direction and the regulations will change once the technical and operational problem are addressed.

Thanks a lot everyone. You have all been very helpful with your answers. I am sure that in the countries in which it's not yet regulated and therefore still not legal, it will soon become regulated. It's just a game of waiting for the legislatures to do their jobs.

The current situation (November 2018) regarding beyond visual line of sight operations (BVLOS) is heterogeneous:

Overall, not allowed in Europe, but there are notable exceptions where BVLOS is explicitly regulated, see below.
Regulated in Canada
Regulated in a few countries in Asia, Africa and Latin America.
Not allowed in the US

US
UAVs fall under Part 107 operations which prevents BVLOS (107.31). Waivers can be requested, but only 27 have been granted to date (enter "107.31" in the search box).
European Union or EASA member states
EASA is the European safety agency. For EASA member states (EU and a few other countries), there are two opposite situations today:
With no surprise North European countries (Iceland, Norway, Sweden), with many isolated locations have allowed BVLOS operations early, including for delivery of goods to consumers, e.g. Aha, an online marketplace, delivers goods using drones in Iceland. Not only this is BVLOS, but it's even automated.
Many countries don't allow it but they are waiting for a EU regulation that would allow them. Actually current opinion of the EASA is it must be allowed (but more for industrial uses than for good delivery to public):

EASA will develop standard scenarios that will make it simpler to
  obtain authorisations for well‑defined operations (such as, for
  example, linear inspections conducted in BVLOS, or crop spraying).

(Source)
In their declaration EASA mentions linear inspections, which has been actually something done in France since a long time for railways catenaries and electric grid lines.
France has kept with its pioneering role in aviation. BVLOS is regulated since 2012. A company located in Toulouse, another well known place for aviation, paved this road. As I'm not going to do their advertising, I let you read about them online, e.g. last year they were able to have a 50-km civilian flight with a 3G data link.
Switzerland
If you are asking for your home country, Switzerland, which is also an EASA member state:

LOS is required, but waivers are possible, though there are no public criteria provided, so you need to try, when you have defined all the details of your project.
As DeltaLima mentioned (maybe with a good insider knowledge) laws are rapidly evolving in the domain, as does UAV technology.
Around the World
Taken from International Commercial Drone Regulation and Drone Delivery Services by Rand Corporation:

For countries that have drone regulations, these regulations typically
  incorporate a pilot’s license, registration of the drone, restricted
  zones, and insurance; regulation requirements vary based on such
  parameters as drone mass, population density, altitude, and use cases.

and the list of countries in 2017:

As visible there are legal possibility for BVLOS in many countries and across all continents.
Permission limits
Same document, excerpt for three countries:

For France already mentioned, we see the BVLOS is authorized up to 1 km for 2 kg+ mass, and unlimited below (but constraints like pilot license and registration still apply). Looking at the criteria for a permissive country:

Well, except height and insurance in certain cases, there is no other ones!
Future market
While B2B application have a large market, the B2C market is huge in an era of online sales and home delivery. Amazon is waiting for (experimentation in Japan), as quick food businesses do, for their delivery.

Iceland is not a member of the EU. It does appear to be a member of the European Economic Area, which is the same status as that of Norway. https://en.wikipedia.org/wiki/Iceland%E2%80%93European_Union_relations This is potentially a bit confusing since you list it under a "European Union" heading.

@aCVn, You're right, they probably wouldn't appreciate being said EU members. That said, the confusion is because they are full EASA member states.

That's clearer.

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What is the correct procedure for operating the engine fire extinguishers on an ATR72?
I am developing an application for airport fire crew and ground staff. Part of the application is to familiarize users with emergency procedures of various aircraft. I have a few questions about the procedure for discharging the engine fire extinguishers on an ATR72 that I hope someone can help me with:

As I understand it, pilot must pull the red handle and twist 90 degrees. This will stop the engine. Pilot must then press the discharge squib button in order to deploy the extinguishers. is this correct?
What would happen if the pilot pressed the discharge squib button before pulling the red handle?
Am I correct in assuming that if the system has detected an engine fire, then the "fault off" buttons would be lit and there would be an audible alarm? If this is the case, would the alarm stop when the discharge squib button is pressed, or only when the fault off button is pressed?
Above the buttons it is written: "Agent 1 Loop A" and "Loop B Agent 2". what does this mean and what is the difference between the two systems? In what circumstances would the pilot have to press both discharge squib buttons or both fault off buttons? In what circumstances would they only have to press one?

As I understand it, pilot must pull the red handle and twist 90 degrees. This will stop the engine. Pilot must then press the discharge squib button in order to deploy the extinguishers. is this correct?

Yes, this is correct, except that the handle does not need to be twisted as far as I know. When the handle is pulled, the following things will happen:

The propeller on this side is feathered.
The fuel LP (low pressure) valve is closed.
The bleed air and HP valves are closed.
The deice and shutoff valve is closed.
The DC and ACW generators are disconnected.
The hydraulic to prop brake is closed on the other engine.

Pressing the squib button will then discharge the extinguishing bottle into the engine.

What would happen if the pilot pressed the discharge squib button before pulling the red handle?

Nothing, the button is not armed at this stage:

AGENT/SQUIB
armed when T handle pulled.
Discharges bottle.
(DC EMER/HOT MAIN BAT)

Am I correct in assuming that if the system has detected an engine fire, then the "fault off" buttons would be lit and there would be an audible alarm? If this is the case, would the alarm stop when the discharge squib button is pressed, or only when the fault off button is pressed?

Yes, both FAULT lights would be on and the alarm is triggered, if both loops A and B detect the fire:

The pilots would be alerted of the fire by:

master WARNING light flashes
ENG 1/2 FIRE light illuminates on the CAP (Crew Alerting Panel)
FUEL SO illuminates on the respective condition lever
respective fire handle illuminates
aural alarm sounds

A single FAULT would indicate a fault in the detection system, not a fire itself:

LOOP/FAULT
change in resistance, inhibits fire signal until turned off.
Loop on CAP (DC emer)

You would press the button to turn off the respective loop such that the other loop can detect a fire alone:

OFF
takes respective loop out of parallel circuit. Allows other loop to activate fire signal alone.

Above the buttons it is written: "Agent 1 Loop A" and "Loop B Agent 2". what does this mean and what is the difference between the two systems? In what circumstances would the pilot have to press both discharge squib buttons or both fault off buttons? In what circumstances would they only have to press one?

There are two fire extinguishing bottles and each can be discharged into either engine (Agent 1 refers to the bottle on the same side and Agent 2 to the one on the other side):

The correct procedure for an IN FLIGHT ENG FIRE is:

PL [Power Lever] affected side ... FI [Flight Idle]
CL [Condition Lever] affected side ... FTR [Feather] THEN FUEL SO
FIRE HANDLE affected side ... PULL
if condition persists after 10 seconds:
AGENT 1 affected side ... DISCH
if condition persists after 30 seconds:
AGENT 2 affected side ... DISCH
LAND ASAP

(ATR 72 QRH)

Source: ATR Systems Training Document
Also have a look at this YouTube video found by Jpe61.

Excellent answer, thank you very much, and thank you for the manual reference too. Just to clarify: if the system detects an engine fire - it alerts the pilot by lighting the lights on the respective engine fire handle? Is there also an audible alarm?

The fire alert consists of master WARNING light coming on, ENG 1/2 FIRE light
on the CAP coming on, the fire light on the respective condition lever coming on, the respective fire handle illuminates and an aural alert. I haven't figured out when the aural alert stops, but typically one can press the master WARNING/CAUTION button to silence the alert (at least that is what I know from other aircraft like a Boeing 737).

@AdrianTaylor before to pulling the fire hande the engine bleed valve should be closed to rule out the possibility of bleed leak causing a faulty fire indication. If this does not solve the predicament, next item would be pulling the affected engine condition lewer back to cut off fuel supply to engine. If this is not done, fuel lines might collapse preventing restart (if for some weird reason you'd want to restart a burned engine). After this you may yank the fire handle.

@Jpe61 I included the relevant checklist from the QRH. It sounds a bit different from what you described. Do you have source for your steps?

@Bianfable got it from youtube, so it might not be the absolute truth :) https://youtu.be/mhWYIjgtRsY

It's pretty much SOP on any engine fire situation to start by cutting off fuel supply as this might very well extinguish the fire, and firing the fire bottle(s) would be unnecessary.

@Jpe61 Interesting, thanks for the link. It looks like a professional training program though.


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What do these symbols mean?

What do these symbols mean in an airport?

The answer is stated in ICAO Annex 12 (Search and Rescue)PDF. (See Appendix I relevant to Chapter 5, 5.8 of the Annex.)
Ground-air visual signal code for use by survivors:

Ground-air visual signal code for use by rescue units:

Note 1.— Symbols may be formed by any means such as: strips of fabric, parachute material, pieces of wood, stones or such like material; marking the surface by tramping, or staining with oil.

Thank you for the answer.

Very interesting.  In "Use of Weapons", Iain M Banks adapts this kind of signalling.  Zakalwe marks his location for airborne pickup on a battlefield by making a Z - by arranging bodies...


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Simple explanation for static and dynamic pressure?
From what I understand, static pressure is just the pressure of still air and acts perpendicular to the airflow and surface. An airplane will feel static pressure regardless of whether it is moving or not. If there was airflow moving through a pipe, then static pressure is the pressure exerted on the walls of the pipe.
On the other hand, dynamic pressure is the pressure that results from the motion of air, or its kinetic energy. It acts parallel to the flow of air. Would it be appropriate to say that dynamic pressure is the pressure exerted on the windward side of a flat plate in the pipe like this:

If this illustration is correct, then does that mean maximum dynamic pressure is felt by a surface when it is perpendicular to the flow?

Does this answer your question? How can dynamic and static pressure be explained?

@Pondlife I saw that thread, but it was still a bit unclear to me about how dynamic pressure is exerted, and when it is at its strongest.

I'm pretty sure that the dynamic pressure would remain the same if you rotated a flat plate, but obviously the total force would increase because it's acting against a larger surface.  One of the engineers here could show you the math...

Static pressure is exactly as you describe it.
Dynamic pressure is not necessarily the pressure on your plate. It is given by the same formula as kinetic energy
1/2 * mass * velocity^2
except instead of "mass", we use "density".
The actual pressure from movement on your plate is given using a number called pressure coefficient, which is just the proportion of the dynamic pressure that your plate actually feels.
So the actual pressure that your plate feels is given by:
Pressure = Pressure coefficient * Dynamic pressure + Static pressure
Your plate could have a pressure coefficient close to one, in which case you could be experiencing near dynamic pressure (+static of course). A very streamlined body might have a very low pressure coefficient, in which case the actual pressure experienced is lower.
And, taking another look at your static pressure example, if you close a valve and stop the flow, the pressure pushing outwards on the pipe will be equal to static pressure + dynamic pressure.
(Yes, the pressure coefficient is related to the drag coefficient)

Static pressure is a force per unit of area due to fluid molecular motion leading to some statistical collisions with its environment (a solid submerged or another fluid for instance). Pressure gives an information of the fluid state (in a thermodynamics sense) and is a « measure » of the force apply by molecules as a whole. Wikipedia could be helpful on that topic.
Dynamic pressure is a bit confusing term as it is the kinetic energy of a fluid parcel (a unit of volume). This parcel has different form of energy (internal, pressure, potential) and this one is energy due to its motion. But it is not a pressure at all and does not act on the solid. However, disturbance created by the body (the flat plate on the picture) will slow down the flow in front, increasing pressure near surfaces. But this is still that pressure difference between front and back which is « felt » by the plate.
In fact, I believe this is the reason why we call it dynamic pressure. It is an energy form (known as kinetic energy) which is easily changed into pressure (or inversely pressure changing to kinetic energy) during fluid dynamics process: drag and lift are created like this on a flow around a body, gas expanding inside jet engine nozzle for thrust generation, etc..


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What does "NON-COMPLIANCE WITH FAR 157" mean for an airport?
I was looking up the airport in Gorham, New Hampshire (2G8) on SkyVector and noticed it had a line that said "NON-COMPLIANCE WITH FAR 157". I know FAR 157 concerns what is needed to build, modify, or decommission a runway. What does this line mean in this context?

Shorthand for "someone screwed up"

@Burke, going to wave camp?

What does "NON-COMPLIANCE WITH FAR 157" mean for an airport?

In short
It means the airfield was not surveyed by FAA (or wasn't resurveyed after a change).
In the US, a landing strip can be opened by anyone, e.g. on their private property, without facilities verification by FAA, but it can be used only within certain limits, e.g. not more than 10 operations per day.
Airfields intended for certain uses, e.g. carrier operations, or instrument flying, and permanent airfields need some verification from FAA, this verification is triggered by filling a request for FAR 157, or for a more stringent framework.

Details
A landing strip which has not been declared to FAA under FAR 157 has limitations set in 157.1 Applicability:

This part does not apply to projects involving:

An airport at which flight operations will be conducted under visual flight rules (VFR) and which is used or intended to be used for a period of less than 30
consecutive days with no more than 10 operations per day.

The intermittent use of a site that is not an established airport, which is used or intended to be used for less than one year and at which flight operations will be conducted only under VFR

There is no obligation to use FAR 157 if these conditions are met.
On the other hand upon reception of the declaration, FAA surveys the neighboring to ensure the airfield is safe to use, and the above limitations are removed.
After the airfield has been declared FAR 157 compliant, FAA will also regulate future changes in the neighboring, e.g. new constructions, or crane erection to maintain the safety.


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Did Lockheed test the TriStar in conditions similar to a century of operation?
I have no source for this claim except a motivational book. I am unable to find anything on Google regarding this.
The claim is that they ran a test on s TriStar that put it through the stresses of one century's worth of operation, and it survived.
I cannot find the book at the moment. Can anyone confirm or deny this?


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How heavy are modern cantilever monoplane wings?
Aircraft need to reduce weight in order to reduce induced drag.  The modern shallow cantilever beam wings carry a massive weight penalty, as most of the material is wasted inefficiency absorbing the bending moment. However, with advancements in materials,  their mass has reduced to the point that parasitic drag benefits outweigh induced drag losses.
But I would like to know how much structural efficiency still influences wing design. Compared to the total empty weight of the aircraft, how heavy are the wings if modern cantilever monoplanes? This includes large airliners and small GA planes. An example of a design from each class is sufficient.

Your use of words "massive weight penalty" suggests  you have a preconceived bias. Cantilever monoplanes have been the preferred configuration since the 1930s.

@EricS Yes I do, for the reason mentioned in the second half of that sentence

Which I disagree with, but I’ll let the experts answer your question.

Study the 1968 Cessan 172 and the 1968 Cessna Cardinal.  Strut braced and cantilever, nearly same empty weight, nearly same payload, speed etc. Cessna though they would get a much larger speed benefit using a scaled down Centurion cantilever wing than they thought, but in any case the weight penalty was not so much once you allow for the weight of lift struts and the additional related structure of a strut braced design.

Massive weight penalty compared to what? Cantilever monoplanes have been the design default for seventy years.

@Pilothead massive weight penalty in terms of wing mass compared to biplanes

Thicker airfoils work better than the thin airfoils used in WWI biplanes. More lift and less drag and only modest if any weight gain.

@Pilothead please don't design anything by default.

Wing structure is roughly 20% of empty weight, which is roughly half of gross weight. I clipped the two sources some time ago and no longer have references.

One way of looking at this (thanks to fine data chart by Pilothead) is wing loading, and it is best based on takeoff weight, speed, and anticipated G loading in manuevers.
Going to the formula Total Drag = CDo + CDi, we can see why many designers pursued flying wings:  theoretically, almost all drag is CDi (induced drag).
Looking at the high lift to drag ratios of airfoils, we can see the "massive weight penalty" pales in comparison to CDo, especially as airspeed increases.
Wings can lift a lot of weight with minimal drag penalty at optimum angle of attack.
The faster you go, the higher the wing loading can be, which means wings are relatively smaller across the board  because lift squares as speed increases.
Additionally, instead of heavy solid "leaf spring" design spars, structures such as D boxes, stressed skin, and "cantilever within a cantilever" beams make for weight  and all important form drag savings.
But does this mean "monoplane"?  Not necessarily.  Early cantilever bi and triplane builders had to add struts so non-believing government ministers would approve and fund their designs.
In all cases, a shorter wing is stronger and rolls faster.  So, with the trend towards very high aspect wings (some with rows of electric motors), we may yet see an X biplane as a "new" design.

Ultimately, the history of the debate was all about engine power and speed.
In the early days engines were pretty pathetic, forcing designers down the braced-wing route, so aerofoils could be made thin with all the stiffness conferred by the bracing.
The thick vs. thin debate over monoplane wings first took reasonably informed shape in the latter part of WWI, when engine powers above 100 hp and speeds above 100 mph became the norm. Thick wings could be made stiffer, reducing or even eliminating the bracing and thus allowing the maximum speed to take full advantage of the powerful engine.
But it was not an open and shut case. For a well-streamlined design with an efficient l/d ratio and a need for speed, such as a scout fighter, the saving in form drag is worth a little induced drag. But for a clumsy bumbling thing with poor l/d, such as a naval torpedo bomber hung about with all kinds of gadgetry, lighter structural weight was the more important.
As engine powers rose inexorably through the next twenty years, they offered the opportunity for ever-increasing speed through thinner wings and reduced form drag. For example the Spitfire owed its success principally to the combination of the 1,000-plus horsepower Merlin engine with an unusually thin wing at 13% t/c ratio. It also had an unusually long chord for a fighter, not only helping to maintain adequate structural depth with that slender profile, but also reducing the stresses in the main forward spar and reducing the wing loading so that it could take off and land slower and out-turn the Messerschmitt Bf 109.
The thick wing advocates fought back, especially for the heavy lifters, and the type lasted right through WWII and into the jet age; check out the Avro Vulcan nuclear bomber.
Indeed, check out the wing root sections of any large modern airliner. Note how these more sophisticated wings are thick at the root where strength with lightness matter most and thin at the tips where drag dominates.
So it's very much horses for courses. Do you want high speed and high manoeuvrability, do you want to heft as much as you can as far as you can, or do you want an optimal blend of speed with payload-range?

Thick wings also provide a place to put fuel.

@EricS Fuel was seldom a significant factor. If you needed a thin wing, you just found room elsewhere.

it might not have been an issue in WWI, but I think it is a pretty big issue by WWII. Hard to imagine a P-51 being about to escort bombers without wet wings.

@EricS The P-51, like the Spitfire, had relatively thin wings: compare them to say the B-29 heavy lifter. Just, the laminar-flow section happened not to be quite as thin. Even so, like the Spit it carried only some of its operational fuel load in the wing; it could not perform its escort duties without drop tanks. The fuel location was thus not critical to the design, just a minor consequence of it.


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Confusing justification for new engines for Bomber B
https://en.wikipedia.org/wiki/Bomber_B

With engines in the 2,000 to 2,500 hp range, twin-engined aircraft would have considerably more surplus power, allowing for much greater payloads. In theory, the more powerful engine would take no longer to produce than a 1,000 hp design, it would simply be larger. By the late 1930s, engines of this sort of power began to be seriously considered and the British and Germans drew up bomber designs based on them.

https://en.wikipedia.org/wiki/Junkers_Jumo_222

The Jumo 222 was a massive and very costly failure. 289 examples of the Jumo 222's were built in total, none of which saw active service. It also served to seriously hamper Luftwaffe piston-engined designs from 1940 to 1942, while many personnel within the Luftwaffe's government-operated technology development offices (like Oberst Edgar Petersen's chain of several Erprobungsstelle installations) and German military aviation corporate engineering departments waited for the Jumo 222 to finally start working. Meanwhile, all calls for four-engine adaptations in place of twin-engine Jumo 222 powered designs were rejected because it was felt it would place too much strain on the German engine industry. In the end there was nothing to show for it, and late in the war the Luftwaffe was flying barely updated versions of their original pre-war designs.

A bigger engine means bigger or more numerous components. Wouldnt either cause significant increase in time?

As a general take on the subject: the ratio of manufacturing time vs. size mostly depends on what is the bottleneck in production.
For a piston engine, or most mechanical devices of comparable complexity, we can assume it will be the part that is hardest to manufacture due to size, complexity and number of work phases. I would assume in piston engines this would be the engine block, which is the largest single component, has to be cast and then machined in several phases with many different machines. Sleeves, plugs etc. may require installation before the engine block is ready. Another such part would be the cylinder heads, while smaller, there are more than one in large engines.
Increasing bore and/or stroke will have vanishingly small effect on casting or machining time. Adding cylinders will also be non issue for casting, and percentually small increase in machinining time. If a "bigger engine" means a totally different design with more cylinder banks for example, the case is of course different.
Production of smaller components such as pistons, rods, valves and such is relatively easy to scale as long as the raw materials are availlable, which in the case of prolonged war is not guaranteed.
Having said that, if I understand the wikipedia quote correctly it claims that producing 2000 to 2500 hp engine would theoretically require same production time as a 1000 hp engine, I must call bs on the claim. Doubling (or more) the power output of an engine is no longer a case of just adding a couple of cylinders or increasing cylinder volume. The engines of that era were already forced induction, so there's not much to gain there without losing reliability.
As the case of the Jumo 222 shows, squeezing a lot of power from a compact engine easily leads to very complex solutions, such as six cylinder banks. That's no longer as fast to produce as a V configuration engine with half the output.

I wouldn't call the Jumo 213 E a "barely updated" version of original pre-war designs (that would be the Jumo 210), but never mind.
There are conflicting opinions why the Jumo 222 failed. It was certainly a very ambitious design, with less frontal area than a BMW 801 but 20% more power, so development was not easy and needed its time. The first models broke their connecting rods in tests and much besides, but eventually it was the RLM bureaucracy which was the main obstacle to the engine being put to use. When a 2000 HP version passed reliability testing, the goalposts were shifted in Berlin and only a 2500 HP version was deemed fit for mass production. Then a 3000 HP version. So production was never allowed to start.
Much more hinged on the Jumo 222. The Junkers 288 was practically designed around it and, being similarly ambitious as Boeing's B-29, also swallowed lots of resources. On paper it was formidable: Easy to produce and maintain, flying at 690 km/h (430 MPH) in 11 km (36,000 ft) of altitude, it would had given Junkers an unassailable technological advantage over all other German airplane companies. Although 35% larger, it required fewer man-hours to build than the Junkers 88 but (on paper) could carry twice the bomb load over twice the distance. Similarly, a Jumo 222-engined FW-190 showed spectacular performance on paper. However, this would had led to a monopoly of Junkers in airplanes and engines, which was resisted by the RLM. One line of argument goes that Junkers was never allowed to live up to its potential to keep competition alive.
With 24 cylinders, the Jumo 222 certainly was more costly to build than a 12 cylinder in-line engine and its compactness also lets me assume extra efforts in production. However, if you consider the DB 610 as the eventual replacement for the Jumo 222, it also had 24 cylinders, so would had been equally costly to produce. On the other hand, the Jumo 211 was a scaled-up version of the Jumo 210 and had twice the power, but similar man-hours in production (which I assume to be the reasoning behind your first quote). Going for more performance without reducing engine speed will, however, force you to add more cylinders, so production cost will eventually go up with performance when starting from a mature, state-of-the-art design.
What the RLM bureaucracy insisted upon was the restriction of even large bombers to only two engines because it was argued that 4-engine bombers would be too costly to produce and would not have a performance advantage. That is probably what the second of your citations tries to hint at.

But how is it possible that a bigger engine takes the same time as a smaller engine

@Abdullah All you need is bigger machinery for production. Especially much of the peripheral work (design documentation, accounting, management) is not affected.

Does that apply to more-cylinder engines? And even if you keep the number constant, won't you have to wait longer for things like heat up.and cool down of parts?

@Abdullah Yes, and the material cost will go up for larger engines, too. But in the great picture those factors are minor. It will cost much more to add a turbocharger to an aspirated 12-cylinder engine than to increase its size by 26%. That's what is needed to double displacement. Just 26%.

With majority of military aircraft engines of that era, one should keep in mind they were already forced induction, so turbocharging would not be an option in doubling power output.

@Jpe61 This was only meant as an example that cylinder counts are not enough to compare engine cost and complexity.

Roger that Engine optimization as such is a tricky subject, almost as tricky as aeromystique


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Why is the Busemann biplane not used?
A Busemann biplane greatly reduces wave drag  It would allow a deeper, more efficient structure to support a wing with less wetted area and thus friction drag. It would seem trivial to tilt the biplane to produce lift. It looks like the next breakthrough after the supercritical airfoil.
So why do we not find this configuration in modern supersonic aircraft? Are there any prohibitive drawbacks?

Flow choking at off-design conditions.

@OrganicMarble didn't prevent multi shock intakes from existing. All you need to do is deflect a control surface to narrow the inlet or widen the exit until the shock is sucked in.

I'm not the one who noticed the problem, I just learned about it back in the 1970s, so it is pointless to argue with me. If you had done any research before posting this question, you would have read about this problem.

@OrganicMarble I have read about it years ago

it would seem trivial to tilt the biplane to produce lift

Apparently, this is where the entire structure of the Busemann biplane would begin to generate a whole new set of shockwaves while also (common to all biplanes) a lot more drag.
The concept appears to be more useful to help explain symmetrical supersonic shockwave patterns in inlets than as a mechanism for (efficient) supersonic flight.
Sonic "boom" mitigation strategies as seen here appear to be focused on directing the shockwave away from the ground and/or splitting it into many smaller waves instead of the classic N wave.
This can be visualized, 3 dimensionally, as trying to arrange a group of rocks in a stream (of non-compressable fluid) to produce as small a wave as possible.
The first step (obviously) would be to streamline the shape, as shown here.  Beyond that one may try to have the sound waves cancel each other out or scatter in different directions.  The "biplane" is but one of these concepts.
Others may be multiple (unstacked) wings and/or lifting bodies with greater Lift/Drag ratios and lower form drag.  The problem remains creating a structure wide enough to hold a sufficient number of passengers for profitable operation.
The Boeing 2707 tried to solve this issue by taking the best available aerodynamic shape and scaling it to larger size.

A Busemann biplane produces massive friction drag, while creating no lift.
Even if modified to produce, optimistically, 1/2 the lift of a normal wing of the same span, it's still going to incur 4 times the friction drag.
This configuration is well-understood and widely used, for instance, in supersonic inlets. It's just not capable of replacing the fuselage (unless onion rings develop an aeronautical civilization) or the wings.